Project Summary Development of a new, filament-based, low-energy, single-pulse cardiac defibrillation technique Cardiac defibrillation is among the most common life-saving procedures performed every year in the United States. However, it has a number of important drawbacks, including being traumatic for the patient, damaging to the tissue in and around the heart, and draining on the battery when an implantable device is used. Recently, major advances have been made in the area of low-energy defibrillation, which has the potential to bypass these drawbacks. However, much of what happens during low- energy defibrillation is still unknown. Thus we have no clear guidance that can suggest how the electrodes should be shaped, placed or configured, what the shock strengths and polarities should be, when the procedure is most likely to be successful, etc. In the proposed project, we investigate a new shock protocol that has shown great promise in computer simulation. The protocol works though a new combination of mechanisms, which together represent a promising direction forwards in low-energy defibrillation research. The method works by employing a shock whose electric field is configured so that it (1) depolarizes the epicardial surface of the heart, which (2) detaches from that surface the filaments around which fibrillatory reentrant action potential waves rotate, which, in turn (3) modifies the shapes of these filaments into ones that dynamically are known to shrink and disappear, thereby terminating the fibrillation. Investigation of this new mechanism could lead to new insight into how low-energy defibrillation currently works, or alternatively, could lead to new low-energy techniques. For this project, we will, through both experiments and computer modeling, (1) study the dynamics of filament detachment from the surfaces of the heart, the key process involved in our early successful studies, (2) investigate the effects of competing processes and features of the heart on the new mechanism, such as spontaneous wave breakup, rotation of the fiber direction within the heart wall, and curvature of the heart surfaces, and (3) assess the effectiveness of the new mechanism in the real heart and real heart geometry. Successful completion of these aims will help direct research in low-energy defibrillation, and also standard cardioversion, to the extent that electric fields are involved in both. As an R15 project, the proposed research will additionally promote research experience for undergraduate students, who will be involved in both the experimental and computational aspects of the work.